Quantitative PET requires knowledge of the intra-patient photon attenuation map in order to relate observed PET emission activity to the actual PET emission activity within the patient. Although the photon attenuation map can be obtained via a separate scan, such separate scanning is clearly undesirable. Accordingly, methods for estimating both emission activity and photon attenuation from PET data have been considered.
One such approach is considered by the present inventors in US 2015/0119694, filed on Oct. 30, 2014 and hereby incorporated by reference in its entirety. In this work, maximum likelihood expectation maximization (MLEM) is considered for the joint estimation of emission activity and photon attenuation from PET data.